Tap-changing system



H. L. COLE ET AL 1,794,945

TAP CHANGING SYSTEM March 3, 1931.

Filgd Aug. 11, 1928 INVENTORS Horace 1.. Cole & Robe/#5. Geo/ye BY & ATFOERNEY Patented Mar. 3, 1931 UNITED STATES PATENT OFFICE HORACE L. COLE AND ROBERT B. GEORGE, OF SHARON,

PENNSYLVANIA, ASSIGNORS TO PENNSYLVANIA TA ZIP-CHANGING SYSTEM Application filed August 11, 1928. Serial No. 298,890.

Our invention relates generally to transformers and particularly to tap changing systems for transfori'ners,

In the application of transformers pro vided with tap changing systems to electric power lines and particularly to the interconnection of transmission lines, it is often desirable to be able to adjust the phase position of the voltages between the interconnected systems without varying the ratio of transformation within the transformers. In tap changing systems for voltage variation a slight phase displacement usually occurs during the tap changing operation, but ordinarily this displacement is so small that it is unnotieeable. However, if a transformer be arranged with a tap changing system for phase control, that is, the control of the phase angle between the voltages of two in t-erconnected systems, it is difiicult to shift the phase of one system relative to that of the other without effecting a substantial variation in the ratio between the voltages of the two systems.

\Ve have provided a transformer system wherein one tap changer is arranged for phase control and another tap changer is arranged for voltage control, so that, by proper manipulation of the two tap changers the ratio of transformation may be changed without changing the phase displacement, the phase displacement may be varied without changing the ratio of transformation, or the phase displacement may be changed simultaneously with a change in the ratio of transformation in the transformer system.

The object of our invention, generally stated, is to provide a tap changing system for a transformer wherein the ratio of transformation in the transformer, or the phase displacement, or both, may be varied.

A further object of our invention is to provide a tap changing system for a transformer wherein the ratio of transformation may be controlled without substantially disturbing the phase relation.

Another object of our invention is to provide a tap changing system for a transformer wherein the phase displacement may be controlled without substantially disturbing the ratio of transformation.

A more specific object of our invention is to provide a polyphase system of auto transformers wherein a winding is connected in delta relation between phases and the phase position of the voltage in the windings varied to change the phase displacement between incoming and outgoing lines.

Other objects of our invention will become apparent to those skilled in the art when the following description is considered in conjunction with the accompanying drawings, in which Figure 1 is a diagrammatic view of a bank of transformers connected to power lines in accordance with our invention.

Fig. 2 is a diagram showing the relation of the various windings of our transformer system in accordance with the direction of voltages in the windings when in their normal position.

Fig. 3 is a vector diagram showing the direction and magnitude of the voltages in the windings of the transformer system connect ed in accordance with Fig. 2.

Fig. 4 is a diagram showing the relation of transformer windings in the system of Fig. 2 when one adjustment has been made in accordance with our invention.

Fig. 5 is a vector diagram showing the direction in magnitude of voltages in the system of Fig. 4.

Fig. 6 is a diagram showing the relation of windings in the transformer system of F igs. 1, 2 and 4 when a second adjustment has been made in accordance with our invention, and

Fig. 7 is a vector diagram showing the direction and magnitude of voltages in the transformer system of Fig. 6.

Referring now to Fig. 1 a bank of transformers 10 is shown interconnecting two powor lines 11 and 12. and it is desired to be able to control the difference in voltages between the power lines 11 and 12 as well as the phase displacement between these voltages.

The bank of transformers 10 comprises three transformer windings 13, 14 and 15, each connecting corresponding phases of the power lines 11 and 12. Each of the transformer windings 13, 14 and15is provided with two tap changing devices, one of which varies the position of connection of the conductors 16, 17 and 18 to the windings 13, 14 and 15, respectively, and the other of which varies the point of connection of the conductors 22, 23 and 24 of the power line 12 to the windings 13, 14 and 15, respectively. A plurality of transformer windings 19, 20 and 21 inductively related to the windings 13, 14, and 15, respectively, are connected in delta relation and have their terminals connected through the conductors 16, 17 and 18 to intermediate points on the windings 13, 14 and 15, respectively, and these points of connection may be varied as mentioned above. The. connections of the windings may be clearly understood by inspection of Figs. 2, 4 and 6, and it may be seen that the voltages in the windings 19,20 and 21 are. proportional to those across the phases of the power lines, and that windings 19, 20 and 21 constitute a delta connection between intermediate points of the windings 13, 14 and 15.

Upon operation of a tap changer mechanism to vary the point of connection of the conductors 22, 23 and 24 to the auto transformer windings 13, 14 and 15, respectively, it will be apparent that the number of effective turns between the conductors 22 and 25 in the winding 13, between the conductors 23 and 26 in the winding 14, and between the conductors 24 and 27 in the winding 15, may be varied, and, in this way, the phase positions of the voltages of the power lines 11 and 12 may be varied as desired. The conductors 22, 23 and 24 may be connected to the windings 13, 14 and 15, respectively, at any number of points to permit a wide range of phase displacement. The voltages prevalent in the various windings with the connection shown in Fig. 2 are represented in Fig. 3, and it will be apparent that upon operation of a tap changer to change the point of connection between conductors 22, 23 and 24 with the auto transformer windings 13, 14 and 15 that the vectors 22-25, 23-26 and 24-27 will be changed in length but not in directio and if it be assumed that the connections s IOWII in the diagram represent the maximum effective turns, then the voltages 22-25, 23-26 and 24-27 are shown at their maximum value in Fig. 3 and variation of the point of connection of the conductors 22, 23 and 24 will decrease the length of the vectors 22-25, 23-26 and 24-27.

The voltage between the phases of the power line 11 is represented by the vectors 25-26, 26-27 and 27-25 and the voltage between phases of the power line 12 is represented by the vectors 22-23, 23-24 and 24-23. It will be apparent that if the length of the vectors 22-25, 23-26 and 24-27 is reduced, that the angle between the vectors 25-27 and 24-22, as well as the corresponding angles for the other phases will also be decreased, and the variation in this angle represents a phase displacen'lent incident to a change in the magnitude of the voltage components represented by the vectors 22-25, 23-26 and 24-27. Although such a change of connections also influences the magnitude of the voltages represented by vectors 24-22, 25-27 and the corresponding voltages in other phases, the magnitudes of all these voltages are varied in the same proportion so that the ratio of transformation is substantially undisturbed.

The positions of the delta connected windings 19, 20 and 21 may be varied relative to the windings 13, 14 and 15 to effect a change in the ratio of transformation. It will be apparent that when the position of the delta connected windings relative to the windings 13, 14 and 15 is altered, as shown in Fig. 4, that the same number of turns exist between phases, but that more turns are energized with power from one phase than are energized with power from another phase, and, in this way, the resultant voltage in the individual windings 19, 20 and 21 of the delta, have their phase position and magnitude changed in accordance with the point of connection to the auto transformer windings 13, 14 and 15. However, no relative phase displacement occurs between the voltages of the power lines 11 and 12 in this case since the phase position of the voltage in each line is shifted the sa-meamount by such a change in connections.

It may be pointed out that the tap changing device employed with a system of thiskind must operate to change the point of connection of the conductors 16, 17 and 18 simultaneously and a corresponding amount in the same direction; the same is also true of the tap changer employed to vary the point of I connection between the conductors 22, 23 and 24 with the transformer windings 13, 14 and 15.

The connection of windings shown in Fig. 4 is the same as that shown in Fig. 2 with the exception that the position of the delta has been changed relative to the auto transformer windings 13, 14 and 15. In other words Fig. 4 shows a transformer system after an adjustment has been made which influences the ratio of voltage transformation in the system and which does not noticeably influence the phase displacement between the terminal voltages of the power lines 11 and 12. Accordingly from Figs. 3 and 5 it will be observed that the vector 27-25 is longer than the vector 27-25, but the vector 24-22 is shorter than the vector 24-22, so that the ratio between the voltages of the lines 11-12 has been varied by the change (if connections. It is apparent that the angle formed by the intersection of vector with vector 27-25 is substantially equal to 23 and 24 be moved to the right connecting the angle formed by the intersection of vectors 2-it-22 and QT*25 so that no phase displacement between the voltages has resulted. It is therefore possible to vary the ratio of voltage transformation in the system by shifting the relation of the delta-connected windings'19, 20 and 21 to the windings 13, 14 and without a substantial disturbance of the phase displacement between the voltages of the systems 11 and 12.

In Fig. 6 the windings are shown after a tap changer has operated to change the point of connection between the conductors 22, 23 and 24 and the auto-transformer windings 13, 14 and 15, respectively, so that the number of effective turns in the auto transformer windings between the power line 11 and the power line 12 have been reduced to vary the phase displacement between the phase voltages of the power lines 11 and 12. \Vith the connection shown in Fig. 6 the other tap changer must have been operated to bring the comtluctors 16, 17 and 18 to the midpoint ofthe effective windings in the auto transformers 13, 14 and 15. This connection has, however, been shown for the sake of clear ness in explaining that the phase displacement between the power lines 11 and 12 may be changed without substantially varying the ratio of voltage transformation in the system.

It will be observed from Fig. 7 that the voltage vectors 24-"27", 2326" and 2i225 are shorter than the vectors 2427, 23Q(3 and 22 25, respectively, but that all the vectors of Fi 7 are proportionally shorter than the vectors of Fig. 3 so that the ratio of transformation is undisturbed as long as the conductors 16, 17 and 18 are connected to the mid-points of windings 19,

20 and 21. It will be. further observed that the angle formed by the intersection of the vectors 2 .-22 and 2T25 is considerably less than the angle formed by the vectors 2l--912 and 27-23. respectively, so that by varying the connections of the conductors 22, 22-5 and 21 with the auto transformer windings 13. 11 and 15, the phase displacement between the voltages of the power lines 11 and 12 may be 'aricd without substantially disturb ing the ratio of voltage transformation in the transformer system.

For a clearer understanding of the operation of our tap changing system. the conductors 16. and 25 may be considered as con nectcd together and s milarly the conductors 17, 223 and 26 as well as 18, 24 and 27. In this case. the windings 1;), 11 and 15 will be by-passcd and the windings l9. Qtl and 21 will be connected across the line as pure impedances. Accordingly. there will be. no phase displacement and the ratio of the voltage of the line 11 to the voltage of the line 1; will he one to one. If the comluctors Q2,

portions of the windings the circuit, a

13, 1t and 15 into phase displacement will occur,

and if the conductors 16, 17 and 18 are alsomoved so that they are continuously connect ed to a point on the windings 13, 14 and 15, respectively, which is midway bet-ween the conductors 22, 23 and 21 and conductors 25, 26 and 27, resp ctively, the ratio of voltages of the lines 11 and 12 will remain aSHOne to one. If, however, the conductors 16, 17 and 18 are not connected to the mid-point of the effective portion of the windings 13, 14 and 15, respectively, a change in the ratio of Voltages will occur, the magnitude and direotion of which will be dependent upon the direction and amount of offset from the midpoint to the connection of the conductors 16, 17 and 18.

By suitable manipulation ofthe two tap changing devices to perform the connections described and shown in Figs. 4 and 6, any desired voltage variation or phase displacement which is within the operating limits of the apparatus may be obtained while" the other is kept constant. Although it is obvious that a slight voltage variation takes place between the connections shown in Fig. 2 and those shown in Fig. 4, it is also apparent that a slight change in phase displacement occurs between the connections shown in Fig. 2 and those shown in Fig. 6, but such differences are well within the normal operating limits of such systems but however, by performing two operations together the discrepancies of the one connection will be compensated for by the discrepancies of the other connection, and by suitable manipulation of the two variable connections, it is readily possible to obtain any desired ratio of transformation or phase displacement without influencing the other.

Since it will be possible to modify the embodiment hereinbefore set forth and adapt it to various applications without departing from the spirit and scope of our invention, it is desired that the foregoing description be construed as merely illustrative and not in a limiting sense.

e claim as our invention:

1. In a transformer system, a. pair of power circuits each comprising a plurality of power circuitconductors and a corresponding plurality of variable windings connected in series circuit relation with said con ductors, a plurality of windings inductively related to said variable windings and each connected between intermediate points of adjacent. variable windings, means for varying the point of connection between said last named and said variable windings, and means for varying the voltage in said variable winding whereby a variation in the phase displacement and in the voltage ratio is obtained between said power circuits.

2. In a polyphase transformer system, two power lines, each comprising a like number of conductors, variable transformer windings connected between corresponding conductors of the two power lines, a bank of transformer windings inductively related to said variable windings and connected together in delta relation and between intermediate points on said variable transformer windings, means for varying the effective turns in said variable transformer windings, and means for varying the points of interconnection between said variable transformer windings and said bank of transformers.

A polyphase transformer bank comprising a plurality of variable windings, a plurality of fixed windings connected between said variable windings and across phases, means for varying the effective number of turns of said variable windings and means for varying the points of connection between said fixed windings and said variable windings whereby the voltage components may be varied. I

4. In a three-phase transformer system, ahigh voltage power line, a low voltage power line, auto transformers connecting the power lines, transformer windings connected in delta relation between intermediate points on the auto transformers, means for varying the point of connection between said windings whereby the effective turns may be varied, and means for varying the number of turns in the auto transformers.

5. In a transformer system, primary and secondary power lines, auto transformers connecting corresponding phases of the power lines, means for varying the auto transformers to vary the phase displacement between voltages of the power lines, a plurality of windings connected between phases and means for varying the turns between phases to vary the ratio of transformation in the system.

6. In a polyphase transformer system, primary and secondary power lines, transformer windings connecting corresponding phases of the power lines, transformer windings connected across phases, means for varying the effective turns between power lines to vary the ratio of transformation, and means for varying the effective turns between phases to vary the phase displacement between power lines.

7. In a polyphase transformer system, primary and secondary lines, transformer windings connecting the lines, transformer windings across phases, and means for varying the voltage per turn in said winding to ,ifect the variation in the ratio of transformation and phase displacement between the voltages of the primary and secondary lines.

8. A three-phase transformer system comprising, in combination, a plurality of windings having out-of-phase voltages, a plurality of windings disposed in delta relation and connected to intermediate points on said first mentioned windings, and means for changing the points of said connection whereby the phase position of the voltage in said last mentioned winding is varied.

In testimony whereof, we. have hereunto subscribed our names this 8th day of August,

HORACE L. COLE. ROBERT B. ononen. 

